The invention relates to the field of liquid handling. More specifically, the invention relates to dispensing devices which dispense sample liquid from a magazine which is inserted into the device and which include a hydraulic pump for collapsing the inserted magazine and dispensing sample liquid therefrom.
For many liquid handling applications both quantitative accuracy and cleanliness are required. The invention is a hydraulic dispenser which includes and combines the means to impart both quantitative accuracy and cleanliness. Quantitative accuracy is provided by the use of a hydraulic press and a hydraulic pump; cleanliness is provided by the use of an insertable magazine for containing the sample liquid. During operation, the insertable magazine is attached to and hydraulically coupled to the hydraulic press. The hydraulic pump within the hydraulic press acts on the coupled magazine in order to dispense sample liquid by means of quantitative positive hydraulic displacement.
The hydraulic press houses hydraulic liquid and includes the means to generate both quantitative positive displacements and reflux displacements of the enclosed hydraulic liquid. The hydraulic press includes a hydraulic pump and a magazine coupler hydraulically connected to one an other. When the insertable magazine and the magazine coupler are connected, the magazine coupler relays hydraulic displacements from the hydraulic pump to the magazine. Hydraulic displacements generated by the pump are relayed through the coupler to the magazine to cause the magazine to expand or to collapse. The magazine can be loaded with sample liquid either prior to insertion or after insertion. Reflux displacements generated by the pump cause an inserted magazine to expand and thereby to aspirate sample liquid; positive displacements generated by the pump cause the magazine to collapse and thereby to express sample liquid. The insertion and connection of a preloaded magazine without entrapped air establishes immediate hydraulic contact with the pump. If a magazine is loaded after insertion, hydraulic contact is established after the entrapped air is purged. The accuracy of dispensing for this invention depends on the accuracy of the quantitative positive displacements generated by the hydraulic pump and upon the establishment of hydraulic contact between the hydraulic pump and the sample liquid contained within the magazine. The accuracy of dispensing for this invention does not depend upon the accuracy of the reflux displacements.
Dispensers utililizing a hydraulic pump hydraulically coupled to a supply chamber for dispensing liquid from the supply chamber are known. Examples of the use of a hydraulic pump for dispensing liquids are illustrated in Guinn U.S. Pat. No. 3,572,552 and Haase U.S. Pat. No. 4,158,035. In each of these devices, the supply chamber is an integral and permanent part of the device. Neither of these devices includes the means to couple to an insertable magazine. Although these devices teach how to establish hydraulic contact between the pump and the diaphragm of the supply chamber, the devices do not teach how to establish hydraulic contact between the pump and the sample liquid enclosed by the supply chamber. The accuracy of these devices depends upon the accuracy of both the reflux displacement and the positive displacement, neither of which is hydraulically coupled to the sample liquid. These devices are not capable of positive hydraulic displacement of the sample liquid.
Positive displacement and reflux displacement should be distinguished. A positive displacement results from the assertion of an affirmative force. If the force underlying a positive displacement is sufficient, it will overwhelm any resistive properties of the sample liquid such as viscosity, surface tension, density, and vapor pressure and any extrinsic forces such as atmospheric pressure or gravity. A reflux displacement results from the force of atmospheric pressure when a pre-existing restraining force is removed. The accuracy of a reflux displacement is limited by the presence of resistive forces which may exceed the forces due to atmospheric pressure.
Positive hydraulic displacement should be distinguished from positive displacement. A positive hydraulic displacement results from the action of a positive force upon a train of mechanical parts and incompressible liquids contained in a rigid container. An initial positive force applied at one end is undissipated by the train. The train is not hydraulic if it includes a compressible component. When a positive force is applied at one end of a compressible train, the train will compress until its compression pressure matches the sum of all opposing resistive pressures. The effect is to dissipate the initial applied force. The displacement force at the far end of a compressible train is less than the initial applied force. Because the Guinn and Haase devices each allow air to be entrapped within their supply chambers, these devices can not be considered to be positive hydraulic displacement devices. All air must be purged from a hydraulic system for the system to be incompressible. Neither the Guinn device nor the Haase device illustrates how to establish hydraulic contact between the pump and the sample liquid.
An example of a device utilizing positive hydraulic displacement is illustrated in Hale U.S. Pat. No. 2,529,937. The Hale device hydraulically couples a displacement liquid with the sample liquid for controlling and metering the flow rate of the sample liquid. The Hale device does not include means for dispensing individual aliquots of the sample liquid or for aspirating sample liquid into the sample chamber. The Hale device does not include a pump or its equivalent which can generate quantitative displacements of the hydraulic liquid. The Hale device is useful for the continuous application of sample liquid at a measured flow rate.
An example of an other device utilizing positive hydraulic displacement is illustrated in Galster U.S. Pat. No. 3,121,614. The Galster device is a titration device which dispenses serial aliquots of identical volumes of standard solution into a test solution. The Galster patent illustrates how to hydraulically couple a pressure liquid with a titrating liquid for dispensing the titrating liquid. However, the Galster patent does not teach the concept of positive hydraulic displacement. Also, the Galster device does not include means to couple an insertable magazine to the pump. The sample chamber of the Galster device must be cleaned by flushing between uses of different titrating liquids.
Dispensers which utilize disposable magazines are known and widely used. The use of a disposable magazine improves the cleanliness and convenience of liquid handling. Disposable magazines are particularly useful for handling corrosive, radio active, and other toxic liquids.
An example of a dispensing device which combines the use of an insertable magazine with a hydraulic pump is illustrated in Begg U.S. Pat. No. 3,736,099. The Begg device is a convenient dispensing device because it combines some of the advantages of a hydraulic pump with the convenience of the insertable magazine. However, the Begg device does not include the means to establish hydraulic contact between the pump and the sample liquid. The Begg patent does not teach how to purge entrapped air from the inserted magazine; the Begg device does not teach how to insert and to connect a preloaded magazine to the dispensing device.